Method and system for television transmission



s. cLo'rHlER Er AL METHOD lAND SYSTEM FOR TELEVISION TRANSMISSION Filedoct; 2o, 1937 May 2l, 1940.'

Patented May 21, 1940 PATENT oFFlcE METHOD AND SYSTEM FOR TELEVISIONTRANSMISSION Stewart L. Clothier, East Orange, and Harold C.

Hogencamp,

Irvington, N.

J., assgnors to Kolorama Laboratories, Inc., Newark, N. J., acorporation of New Jersey Application October 20, 1937, Serial No.169,958

2 Claims.

Our invention relates to improvements in methods and systems fortelevision transmission.

One of the present, accepted methods in television broadcasting is toemploy a transmitter for sending the synchronizing and the video orpicture signals on an ultra high frequency carrier wave, and to employanother transmitter, operating entirely independently of the other, forsending the sound signals also on an ultra high frequency carrier wavewhich,l however, is separated from the first-mentioned carrier wave by3.25 mc. The two transmitters have their own, separate oscillators forgenerating the two respective ultra high frequency carrier waves. Theseoscillators are entirely disassociated from and operate entirelyindependentlyof each other.

At the receiving station. in selecting a Ygiven television broadcastingstation it is the practice to adjust the receiver for the best soundreception, in which case the receiver is .automatically adjusted for thebest television reception. This is accomplished by virtue of the factthat rthe conventional receiver embodies a common oscillator and twoindependent intermediate-frequency amplifiers. These twointermediate-frequency amplifiers are adj-usted to twointermediate-frequency bands whose separation is 3.25 mc. This manner ofoperation is dependent upon the accuracy with which the fixedrelationship between the two ultra high frequency broadcast carriers ismaintained, and for this purpose, complicated and expensive frequencycontrol equipment has heretofore been required to keep the two carriersfixed at the respective frequencies, or at least close enough so thatthe separation does not vary far enough from 3.25 inc. to cause poortelevision reception atthe receiver. The difliculty, in this connection,becomes apparent when it is realized that a variation of only .05% ineach of the two transmission carrier frequencies might cause a maximumvariation of nearly 50 k. c. in the separation between the twofrequencies when the two carrier frequencies are, for example, 48 mc.and 51.25 rnc. respectively. and the intended, constant separationtherefore 3.25 mc.

With the foregoing in mind, it is one of 4the objects of our inventionto provide an improved method and system for television transmissionrwhich avoids the disadvantages referred to in the methods and systemsused heretofore. and, particularly, which eliminates the necessity forthe use of complicated and expensive frequency control equipment formaintaining constant the operating action of the two oscillators forobtaining the two ultra high frequency carrier waves.

Another object of our invention is the provision of an improved methodand l.system for television transmission by which a fixed relationshipand separation between the two ultra high frequency transmissioncarriers is maintained in a reliable and eicient manner.

Other objects and advantages will hereinafter appear.

In accordance with our invention, two independently operatingtransmitters are used to transmit, respectively, the picture and soundsignals, the frequency of operation ofone of the transmitters iscontrolled by a first oscillator operating at a fixed frequency, and thefrequency of operation of the other transmitter is controlled by thejoint effect of said oscillator and a second oscillator operating at afixed frequency.

More particularly, in accordance with our invention, a master,crystal-controlled oscillatorzis lused to develop a substantially fixed,ultra high frequency carrier Wave on which picture and synchronizingsignals are broadcast by a first transmitter. A mixer circuit issupplied with this ultra high frequency and also with the frequency fromthe output circuit of a second crystal-cone trolled oscillator operatingat a substantially fixed frequency different from said first-namedfrequency, whereby there is developed a second ultra high frequencycarrier wave, the frequency of which is the algebraic sum of therespective frequencies in said output circuits. It is on this second,ultra high frequency carrier wave that the sound signals are broadcastby a second transmitter operating independently of the firsttransmitter. a

Our invention resides in the novel method and combination of characterhereinafter described and claimed.

For the purpose of illustrating our invention, an embodiment thereof isshown in the drawing, in which:

Figure l is a block diagram of a television broadcasting systemconstructed and operating in accordance with our invention; and

Fig. 2 is a schematic representation of the television channel in whichthe system in Fig. l-opcrates.

With reference to the drawing, the numeral lli designates a iirsttransmitter and power amplifier supplied with synchronizing signals andvideo or picture signals by the units shown and which are constructedand combined in a conventional manner. These units are a video pick-updevice Il, an amplifier I2 for the video signals, a modat 3.25 mc.

ulator I3, a generator Ill for producing the synchronizing signals, andan amplifier l5 for the synchronizing signals.

The reference numeral I6 designates a second transmitter and powei`amplifier operating independently of the first and supplied with soundsignals by a sound pick-up device l', an amplifier i8 for the soundsignals, and a modulator i9, all constructed and combined in aconventional manner.

The frequency 0f operation of the first transmitter l is controlled by afirst, crystal-controlled, master oscillator 2D operating at a fixedfrequency of 12 mc. for example. This frequency is doubled to 24 mc. bya frequency doubler 2l, and again doubled to 48 mc. by a secondfrequency doubler 22, whereby a 48 mc. television carrier wave isdeveloped. It is on this ultra high frequency carrier wave, which isamplified by an amplifier 23 and supplied to the television transmitterIll, that the picture and synchronizing signals are broadcast.

In lieu of using a second, independent, and ultra high frequencyoscillator for controlling the sound transmitter I6, as heretofore, weemploy a crystal-controlled oscillator 24 operating at a fixed frequencymaterially lower than the fre,- quency of operation of the masteroscillator 20. That is, in the particular embodiment of our inventiondisclosed, the second oscillator 24 operates at the fixed frequency of3.25 mc., as against the frequency of 12 mc. at which the masteroscillator 2Q operates.

A mixer circuit 25 is supplied from the output circuits of both themaster oscillator 20, after multiplying to the desired ultra highfrequency, and the second oscillator 24, whereby there is developed asecond carrier wave the frequency of which is, in this case, the sum ofthe respective frequencies in said output circuits, that is, 51.25 mc.It is on this second, ultra high frequency carrier wave, which isamplified by an amplifier 2S and supplied to the transmitter I 6, thatthe sound signals are broadcast.

Since the frequency of operation of the second oscillator 24 isrelatively low, variations in its output frequency represent but anegligible percentage of the 3.25 mc. as compared to what wouldotherwise be the case if this oscillator operated at the ultra highfrequency of 51.25 mc. to develop the sound carrier independently of theiirst oscillator 20, as heretofore. For all practical purposes,therefore, it can be said that the operation of the second oscillator 24remains fixed Therefore, although the frequency of operation of themaster oscillator might vary, the separation of the television and soundcarriers will remain substantially fixed since this separation in ourimproved method and system is always the frequency of operation of thesecond oscillator 24.

If it is desired that the sound carrier be lower in frequency than thetelevision carrier by the 3.25 mc. separation, the mixer circuit 25 ismade to subtract the frequency of the second oscillator 24 from theultra high carrier frequency developed by the master oscillator 20. Inother words, the frequency of the sound carrier is in any case thealgebraic sum of the respective frequencies in the output circuits ofthe two oscillators.

An example of a mixer circuit for combining the frequencies of twooscillators is given in the publication Radio, issues of June and July,1936.

From the foregoing it will be seen that in our improved method andsystem, separation between the ultra high frequencies of the televisionand sound carriers is maintained constant in a relatively simple andeiiicient manner, and regardless of occurring variation in the frequencyof operation of the master oscillator for developing the televisioncarrier.

While but one embodiment of our invention has been disclosed, it will beunderstood that various modifications, within the conception of thoseskilled in the art, are possible without departing from the spirit ofour invention or the scope of the claims. For example, any othersuitable means may be employed for developing the ultra high frequencytelevision carrier wave, instead of a crystal-controlled oscillator andthe associated frequency doublers. Likewise, any suitable, stable,separation oscillator may be used, although we prefer the use of acrystal-controlled oscillator for this purpose.

We claim as our invention:

l. A television transmission system comprising a first radio frequencytransmitter including an antenna system, means including an oscillatorfor developing a rst ultra-high frequency carrier Wave and means formodulating said first carrier wave at audio frequencies; a second radiofrequency transmitter including a separate antenna system, meansincluding a separate oscillator for developing a second ultra-highfrequency wave differing infrequency from the first carrier wave, andmeans for modulating said second carrier Wave at video frequencies; oneof said oscillators being crystal-controlled and operated at the dcsiredseparation frequency and interlocking and maintaining a fixed separationin frequency between the two carrier waves.

2. In a television transmission system, a rst transmitter including anantenna system, means for developing and supplying picture signals tosaid transmitter, a second transmitter operating independently of saidfirst transmitter and including a separate antenna system, means fordeveloping sound signals and supplying the same to said secondtransmitter, means comprising a crystal-controlled master oscillatoroperating at a substantially fixed frequency and developing' an ultrahigh frequency carrier wave supplied to said first transmitter, meanscomprising a second crystal-controlled oscillator operating at asubstantially fixed frequency materially lower than said first-namedfrequency, and a mixer circuit supplied from the output circuits of bothsaid oscillators and operating to develop a second carrier wave thefrequency of which is the algebraic sum of the respective frequencies insaid output circuits, said second carrier wave being supplied to saidsecond transmitter, said respective carriers thereby being interlockedand maintained separated by the constant frequency of said secondcrystal-controlled oscillator.

STEWART L. CLOTHIER. HAROLD C. HOGENCAMP.

